Add child-bounties pallet. (#10309)

* Extract child-bounties as a separate pallet.

* Initial tests added.

* More tests.

* Tests complete. Fixed curator fee issue.

* Fixed comments.

* Added benchmarks for child-bounties pallet.

* Added weights.

* Fixed formatting.

* Fixed comments.

* Re-run benchmarks for bounties pallet.

* Make cargo fmt happy again

* add max encoded len

* use event structs

* fmt

* fix compile

* Addressed review comments.

* Use config type instead of const in benchmarking.

* Addressed more review comments.

* Use ensure_can_withdraw instead of just checking min balance.

* fmt.

* Introduce ChildBountyCuratorDepositBase to avoid zero curator deposits for child bounties.

* Fix unassign curator logic for child-bounties.

* Added more tests for unassign curator.

* Reduce bounty description max length in node runtime.

* Updated weights for child bounties pallet.

* reduce indentation of unassign_curator

* more indentation reduction

* deduplicate slashing arms

* reintroduce ensure check

* add assertion to check that bad unassign origin fails

* formatting

* Updated comments.

Co-authored-by: Ricardo Rius <ricardo@parity.io>
Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>
Co-authored-by: Alexander Popiak <alexander.popiak@parity.io>

substrate/Cargo.lock

@@ -4702,6 +4702,7 @@ dependencies = [
  "pallet-bags-list",
  "pallet-balances",
  "pallet-bounties",
+ "pallet-child-bounties",
  "pallet-collective",
  "pallet-contracts",
  "pallet-contracts-primitives",
@@ -5383,6 +5384,25 @@ dependencies = [
  "sp-std",
 ]
 
+[[package]]
+name = "pallet-child-bounties"
+version = "4.0.0-dev"
+dependencies = [
+ "frame-benchmarking",
+ "frame-support",
+ "frame-system",
+ "log 0.4.14",
+ "pallet-balances",
+ "pallet-bounties",
+ "pallet-treasury",
+ "parity-scale-codec",
+ "scale-info",
+ "sp-core",
+ "sp-io",
+ "sp-runtime",
+ "sp-std",
+]
+
 [[package]]
 name = "pallet-collective"
 version = "4.0.0-dev"